Objective: Studies in rodents indicate a role of vitamin D in male reproduction but the relationship between vitamin D and androgen levels in men is largely unexplored. We aimed to investigate the association of 25-hydroxyvitamin D [25(OH)D] levels with testosterone, FAI (free androgen index), and SHBG. Moreover, we examined whether androgen levels show a similar seasonal variation to 25(OH)D.

Design: In this cross-sectional study, 25(OH)D, testosterone, and SHBG levels were assessed by immunoassay in 2299 men who were routinely referred for coronary angiography (1997-2000).

Measurements: Main outcome measures were associations of 25(OH)D levels with testosterone, SHBG, and FAI. FAI was calculated as testosterone (nmol/l)/SHBG (nmol/l)×100.

Results: Men with sufficient 25(OH)D levels (≧30 μg/l) had significantly higher levels of testosterone and FAI and significantly lower levels of SHBG when compared to 25(OH)D insufficient (20-29.9 μg/l) and 25(OH)D deficient (<20 μg/l) men (P<0.05 for all). In linear regression analyses adjusted for possible confounders, we found significant associations of 25(OH)D levels with testosterone, FAI, and SHBG levels (P<0.05 for all). 25(OH)D, testosterone, and FAI levels followed a similar seasonal pattern with a nadir in March (12.2 μg/l, 15.9 nmol/l, and 40.8, respectively) and peak levels in August (23.4 μg/l, 18.7 nmol/l, and 49.7, respectively) (P<0.05 for all).

Conclusion: Androgen levels and 25(OH)D levels are associated in men and reveal a concordant seasonal variation. Randomized controlled trials are warranted to evaluate the effect of vitamin D supplementation on androgen levels.